One vertex per element, one color per generator, with an edge from x to x·s.
(1,2)(3,7)(4,6)(5,8)(10,15)(11,18)(12,14)(16,23)(19,20)(22,24)(25,26)(27,30)(28,31)(29,32)(33,37)(34,36)(35,38)(39,40) involution — undirected(1,3,4,8)(2,5,6,7)(9,10,13,15)(11,16,20,22)(12,21,14,17)(18,24,19,23)(25,27)(26,30)(28,33)(29,34)(31,37)(32,36)(35,39)(38,40)(9,11,13,20)(10,16,15,22)(12,18,14,19)(17,23,21,24)(28,35)(30,36)(31,38)(33,39)(2,6)(5,7)(9,12,13,14)(10,17,15,21)(11,19,20,18)(16,24,22,23)(25,28,29,35)(26,31,32,38)(27,33,34,39)(30,37,36,40)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.